Download 6.1: Digestion

Digestion (6.1)
Why digestion occurs (6.1.1)
Role of enzymes (6.1.2)
• Most food is in the form of large complex
molecules which are insoluble and
chemically inert
• Enzymes lower the activation energy for
chemical reactions without being
consumed as part of the reaction
• Allows digestion of food molecules to
occur at body temperatures
• Increases rate at which food is digested
• Breaking food down (digestion):
- Makes it soluble & able to be absorbed
- Generates usable building blocks
Examples of enzymes (6.1.3)
Type
Example
Source
Substrate
Product
Optimal pH
Amylase
Salivary
amylase
Salivary
glands
Starch
Maltose
pH ~7
(neutral)
Protease
Pepsin
Stomach
Protein
Short
polypeptides
pH ~2
(acidic)
Lipase
Pancreatic
lipase
Pancreas
Triglycerides
Glycerol
3 x fatty acid
pH ~8
(alkaline)
Diagram of digestive system (6.1.4)
salivary glands
oesophagus
mouth
liver
stomach
gall
bladder
pancreas
large intestine
small intestine
anus
Role of stomach and the gut (6.1.5)
Stomach
• Temporary storage tank
• Chemical digestion with acids & enzymes
• Makes a creamy paste called chyme
Small Intestine
• Absorption of nutrients
• Lined with villi for ↑SA:Vol ratio
• Bile secreted into small intestine
• Intestinal crypts aid digestive process
Large Intestine
• Absorbs water & dissolved minerals
• Semi-solid faeces eliminated via anus
Distinguish between (6.1.6)
Explain the role of the villus (6.1.7)
Absorption: The movement of fluids or
dissolved substances (e.g. nutrients)
across a cell membrane
Remember: MR SLIM
Assimilation: The conversion of
nutrients into fluid or solid parts of an
organism
Microvilli (↑ SA:Vol ratio for absorption)
Rich capillary network (more efficient transport)
Single-layer epithelium (short diffusion distance)
Lacteals (absorption of lipids)
Intestinal crypts (secretes juice to aid absorption)
Membrane proteins (facilitated diffusion)